Q: When vehicle getting hot it starts to idle higher to 1200 rpm

Hey there. This may be a sign of a failing idle air control valve. The idle air control valve is located on or near your intake manifold that monitors the air intake as it is mixed with fuel prior to being injected into the engine. This valve is controlled by the vehicle’s computer which will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed.

However, when the engine RPM drops below the normal range of 800 RPM (for most cars), it is more than likely that you are dealing with an IAC valve problem. In cases where this valve is clogged or is failing, your vehicle will stall instead of slowing to an idle after the release of the throttle. This may also be related to a cold start enrichment issue as well. When the engine intake air temperature reaches a certain level of heat, the computer will automatically change the air/fuel mixture to adapt to this change in air density. I would recommend having an expert from YourMechanic come to your home to replace your idle air control valve.